Agricultural equipment, construction machines, street sweepers, and like machines are provided with enclosures or cabs to separate the operators of these machines from the outside dirty air. Air processing and ventilating systems have been used with the cabs to provide clean cool air to the inside operator's compartment of the cabs. Examples of vehicle cabs having air ventilating units as described are Grasseler in U.S. Pat. No. 3,532,377 and Doll et al. in U.S. Pat. No. 3,868,896. The Grasseler air treating unit uses a motor-driven fan to move air through a water spray and filter. Air-borne particulates are collected in the water and filter. The Doll et al. air ventilating structure is part of the roof of the cab and uses a pair of motor-driven blowers to force air through fiber-like filters.
Fans having motor-driven blades are used to deliver filtered air to desired locations. Frame structures mount the motors in the center of the fans so that the drive shafts of the motors can be used to support the fan blades. Fiber filters carried by the frame structure and located downstream of the blades separate foreign matter from the air. Examples of this type of filter fans and air cleaning apparatus are disclosed by de Bothezat in U.S. Pat. No. 1,794,447; Steinmetz in U.S. Pat. No. 3,407,570; Jackson in U.S. Pat. No. 3,362,416 and Kile in U.S. Pat. No. 3,593,499.